1. Field of the Invention
This application is related to radio access networks involved in wireless telecommunications, and particularly relates to an internal interface (such as the Common Public Radio Interface (CPRI)) of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station.
2. Related Art and Other Considerations
In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station. A cell is a geographical area where radio coverage is provided by the radio equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The radio base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a control node known as a base station controller (BSC) or radio network controller (RNC). The control node supervises and coordinates various activities of the plural radio base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which, at least in some respects, builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs).
In many radio access networks the radio base station is a concentrated node with essentially most of the components being located at concentrated site. In the future mobile network operators may be afforded more flexibility if the radio base station is configured with a more distributed architecture. For example, a distributed radio base station can take the form of one or more radio equipment portions that are linked to a radio equipment control portion over a radio base station internal interface.
One example of an internal interface of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station is the Common Public Radio Interface (CPRI). The Common Public Radio Interface (CPRI) is described in Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004), and which are incorporated by reference herein in their entirety.
The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) describe a standardized start-up procedure which is supposed to accomplish two main objectives. The first objective is synchronization of the physical layer (layer 1), e.g., byte alignment and hyperframe alignment. The second objective is to align the capabilities of the radio equipment controller (REC) and the radio equipment (RE), particularly with respect to line bit rate, C&M (control and maintenance) link speed, C&M protocol, and vendor specific signaling. According to the specification, since there is no mandatory line bit rate of C&M link speed, the radio equipment controller (REC) and radio equipment (RE) must, during the start-up procedure, try different configurations until a common match is detected.
FIG. 11 illustrates the start-up states and transitions for the standardized start-up procedure discussed in the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004). FIG. 11 shows start-up states A through F, and sixteen possible transitions into or between states A through F. These states and transitions are applicable to each of the radio equipment controller (REC) portion and the radio equipment (RE) portion of the radio base station (RBS).
In state A, the RBS portion waits to be configured to start-up the internal interface, there thus far being no reception or transmission on the internal interface. In conjunction with state A, the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) mention that the operator may configure a suitable start-up configuration (e.g., line bit rate, C&M link characteristics), and that the radio equipment controller (REC) and radio equipment (RE) may also have knowledge about a previous successful configuration.
In state B, an “available set” of line bit rate, protocol revisions, and C&M plane characteristics are known. According to the standard, this may be the complete set of the unit or a subset based on operator configuration or previous negotiation between the units (e.g., from state E). In state B the line bit rate of the interface is determined and both the radio equipment controller (REC) and the radio equipment (RE) reach a certain layer 1 synchronization.
The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) state that the transition 1 from state A to state B is out of the scope of the specification, indicating that a set of available line bit rates, protocol revisions, and C&M link bit rates shall be available (the “available set”). The specification states that this may be the equipment full capabilities or a subset determined by the equipment configuration (manual) or knowledge from previous successful configurations.
The Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) further prescribe a layer 1 start-up timer. If the layer 2 start-up timer expires, transition 16 takes place and state B is entered, possibly modifying the available set of line bit rates and protocols.
Thus, Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) specify a standard start-up procedure with automatic negotiation of an “available set” of protocol and line bit rate. The standard start-up procedure as shown in FIG. 11 can be viewed as an “inner loop”. The standard start-up procedure requires an “outer loop” of operations which is to provide the “available set” for the “inner loop” to use for negotiation. This “outer loop”, which provides the “available set” for use in inner loop negotiations, is outside the specification.
The standard start-up procedure as prescribed by the Common Public Radio Interface Specification Version 1.0 (Sep. 26, 2003) and Version 1.1 (May 10, 2004) have some disadvantages. As a first disadvantage, the standard start-up procedure takes a long time if there are many line bit rates. As a second disadvantage, the standard start-up procedure can hang if the negotiation agrees upon a line bit rate and protocol for which no common C&M links are supported. A third disadvantage is that, when a line bit rate change is required, such a change must be executed very quickly, thereby imposing difficult requirements on the hardware.
What is needed therefore, and an object of the present invention, is a technique for supplying an available set of line bit rate and protocol to a start-up procedure for an internal interface of a distributed radio base station.